Powered down selection of a preferable wireless communications service provider in a multi-service provider environment

ABSTRACT

A powered down communication device locates a wireless service provider in a multi-service provider environment by examining frequency bands while powered down until a frequency band having an acceptable service provider is located. The frequency bands are examined in an order specified by a stored search schedule. An acceptable service provider is identified by comparing the identity of a service provider specified by an identifier received from a band being examined with a list of acceptable service providers. The communication device then registers with the acceptable service provider when powered up.

CROSS REFERENCE TO RELATED INVENTION

This application is related to commonly assigned and concurrently filedU.S. Patent Applications entitled “A Method For Selecting A WirelessCommunications Service Provider In A Multi-Service ProviderEnvironment”, A Method For Selecting a Preferable WirelessCommunications Service Provider In a Multi-Service Provider Environment,and Method For Selecting a Wireless Service Provider In a Multi-ServiceProvider Environment Using a Geographic Database Serial Nos. 08/570,905filed Dec. 12, 1995 now abandoned, 08/570,904 filed Dec. 12, 1995, and08/570,903 filed Dec. 12, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communications; more specifically,communications in a multi-service provider environment.

2. Description of the Related Art

FIG. 1 illustrates a portion of the radio frequency spectrum. Frequencyrange 10 centered around 800 MHz has historically been known as thecellular frequency range and frequency range 12 centered about 1900 MHzis a newer defined frequency range associated with personalcommunication services (PCS). Each range of frequencies, i.e., thecellular and PCS, are broken into two portions. In cellular frequencyrange 10, there is uplink portion 13 which is used for communicationsfrom a mobile communication device to a base station such as a cellularbase station. Portion 16 of cellular frequency range 10 is used fordownlink communications, that is, communications from a cellular basestation to a mobile communication device. In a similar fashion, Portion18 of PCS frequency range 12 is used for uplink communications, that is,communications from a mobile communication device to a base station.Portion 20 of PCS frequency range 12 is used for downlinkcommunications, i.e., communications from a base station to a mobilecommunication device.

Each of the frequency ranges are broken into bands which are typicallyassociated with different service providers. In the case of cellularfrequency range 10, frequency bands 30 and 32 are designated band “a”for uplink and downlink communications, respectively. In a particulargeographic area, a cellular service provider is assigned frequency band“a” in order to carry out mobile communications. Likewise, in the samegeographic area another cellular service provider is assigned frequencybands 34 (uplink) and 36 (downlink) which are designated band “b”. Thefrequency spectrums assigned to the service providers are separated soas to not interfere with each other's communications and thereby enabletwo separate service providers to provide service in the same geographicarea. Recently, the US Government auctioned the PCS frequency spectrumto service providers. As with the cellular frequency range, the PCSfrequency range is broken into several bands where a different serviceprovider may use a particular frequency band for which it is licensedwithin a particular geographical area. The PCS bands are referred to asA, B, C, D, E and F. The A band includes uplink band 50 and downlinkband 52. The B band includes uplink band 54 and downlink band 56. Band Cincludes uplink band 58 and downlink band 60. Each uplink and downlinkband of the A, B and C bands are approximately 30 MHz wide. The D bandincludes uplink band 62 and downlink band 64. The E band includes uplinkband 66 and downlink band 68. Likewise, band F includes uplink band 70and downlink band 72. The uplink and downlink bands of bands D, E and Fare approximately 10 MHz wide each. It should be noted that with thecellular and PCS frequency bands, it is possible to have as many aseight different wireless communication service providers in a particulararea.

Each of the different cellular and PCS bands consist of control channelsand communication channels in both the uplink and downlink direction. Inthe case of analog cellular bands, there are 21 control channels forboth the “a” and “b” bands. Each of the control channels include anuplink and a downlink portion. The control channels transmit informationsuch as an SOC (System Operator Code), an SID (System Identifier Code),paging information call setup information and other overhead informationsuch as information relating to registering with the mobilecommunication system. The portion of the cellular band's spectrum notoccupied by the control channels is used for communication channels.Communication channels carry voice or data communications, where eachchannel consists of an uplink and downlink communications link.Presently there are several cellular communication standards. An analogstandard known as EIA/TIA 553 was built upon the AMPS (Advanced MobilePhone Service) standard. This standard supports 21 analog controlchannels (ACC) and several hundred analog voice or traffic channels(AVC). A newer standard is the EIA/TIA IS54B standard which supportsdual mode operation. Dual mode operation refers to having an analogcontrol channel, and either an analog voice/traffic channel or a digitaltraffic channel (DTC). The AVC or DTC are used for actualcommunications, and the ACC is used to transfer information relating to,for example, call set-ups, service provider identification, and theother overhead or system information.

A newer standard, the EIA/TIA IS136 standard supports communicationscovered by both analog and dual mode cellular, and also includes atotally digital communication scheme which was designed for the PCSfrequency bands A-F and cellular frequency bands “a” and “b”. Thisstandard allows for a digital traffic channel (DTC) and a digitalcontrol channel (DCCH). In the case of the DTC, not only is the voice ordata communicated, but in addition, a digital channel locator (DL) istransmitted in the DTC. The DL enables a mobile communication devicethat locks onto the DTC to use the information in the DL to locate aDCCH for purposes of obtaining information such as the SOC, SID, paginginformation, and other system overhead information carried on thedigital control channel.

When a mobile communication device such as a mobile telephone attemptsto register with the service provider, it locks onto a control channeland reads information such as the SOC and SID. If the SOC and/or SIDcorrespond to a service provider with which the user has a communicationservices agreement, the telephone may register with the serviceprovider's mobile communication system via the up-link control channel.

FIG. 2 illustrates a map of the United States illustrating cities suchas Seattle, Chicago and Washington, D.C. For example, in Seattlefrequency band A has been licensed to SOC (Service Operator Code) 001with a SID of 43 and band C has been licensed to SOC 003 with a SID of37. In Chicago, suppose that frequency band C has been licensed to SOC001 with a SID equal to 57, and that band B has been licensed to SOC 003with a SID of 51. In Washington, D.C. suppose that frequency band “a”has been licensed to a SOC 001 with a SID of 21, and that band A hasbeen licensed to SOC 003 with a SID of 17. It should be noted that thesame SOC may be found in several different locations although ondifferent frequency bands. It should also be noted that the same SOCwill be associated with different SIDs in each geographical area andthat in the same geographic area different service providers havedifferent SIDs. If a particular subscriber to a wirelesstelecommunication service has an agreement with a service providerhaving a SOC of 001, that subscriber would prefer to use systems with aSOC of 001 because the subscriber is likely to receive a less expensiverate. When the subscriber is in Seattle he/she would prefer to be onband A, and if in Chicago on band C, and if in Washington, D.C. on band“a”. The above described situation presents a problem for a wirelesscommunication service subscriber. As a subscriber moves from one area ofthe country to another, the telephone when turned on, searches for the“home” service provider, or the service provider with which thesubscriber has a pre-arranged agreement. If for example, the subscribertravels from Seattle to Chicago, when turning the phone on in Chicago,the phone will search through the different bands of the spectrum toidentify the service operator with the code 001 in order to find thedesired service provider.

In order to find a particular service provider, the phone may have tosearch through both the “a” and “b” cellular bands, and through theeight PCS bands. It should be recalled that there are up to 21 differentACCs in each of the “a” and “b” cellular bands. It may be necessary tocheck 42 ACCS in order to find an ACC from which a SOC or SID may beobtained. Additionally, searching for a particular SOC or SID in PCSbands A through F is particularly time consuming. The digital controlchannels (DCCHs), which contain the SOC and SID, are not assigned tospecific frequencies within a particular PCS band. As a result, themobile communication device may find it necessary to search through thespectrum of each PCS band looking for a DCCH, or an active DTC that hasa digital channel locator (DL) which will direct the mobilecommunication device to the DCCH. As illustrated above, the process ofsearching for a particular service provider is laborious and may requirea period of time on the order of several minutes.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method for locating aparticular or desirable communications service provider in anenvironment having a plurality of service providers. After power-up, amobile communications device such as a cellular telephone, checks themost recently used control channel to determine whether an optimalservice provider is available on that channel. If an optimal serviceprovider is not available or if that channel is not available, themobile communication device performs a search through frequency spectrumin a pre-determined order until an optimal or acceptable serviceprovider is located.

In another embodiment of the invention, the frequency spectrum issearched in a pre-determined order that changes based on informationentered by a mobile communication device distributor or mobilecommunication device user. In yet another embodiment of the invention,the pre-determined order for searching the spectrum for serviceproviders is updated by over the air programming. In still anotherembodiment of the present invention, the pre-determined order forsearching is based on the mobile communication device's operationalhistory.

In yet another embodiment of the present invention, the communicationdevice tunes to a first frequency band and receives a geographicidentifier from the service provider operating in the first frequencyband. The received geographic identifier is compared to a listing ofstored geographic identifiers in order to attempt to locate a matchingstored geographic identifier. Each of the stored geographic identifiersare associated with a desirable frequency band having a desirableservice provider. If comparing the received geographic identifier withthe matching stored geographic identifiers does not produce a match,frequency bands are examined until a second frequency band having adesirable service provider is located. The listing of stored geographicidentifiers is then updated so that the second frequency band isassociated with the received geographic identifier.

In still another embodiment of the present invention, the communicationdevice locates a wireless service provider by examining frequency bandswhile powered down. The frequency bands are examined in an orderspecified by a stored search schedule until a frequency band having anacceptable service provider is located. An acceptable service provideris identified by comparing the identity of a service provider specifiedby an identifier received from a band being examined with a list ofacceptable service providers. The communication device then registerswith the acceptable service provider when the device is powered up.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the frequency spectrum used for wirelesscommunications;

FIG. 2 illustrates service areas within the United States;

FIG. 3 is a block diagram of a mobile communication device;

FIG. 4 is a flow chart illustrating a spectrum searching routine;

FIG. 5 is a flow chart illustrating the global spectrum search routine;

FIG. 6 is a flow chart illustrating a periodic search routine;

FIG. 7 is a flow chart illustrating a received signal strength searchroutine;

FIG. 8 illustrates a search schedule;

FIG. 9 illustrates a prioritized list of service providers; and

FIG. 10 illustrates a list of geographic identifiers and prioritizeddesirable frequency bands.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 illustrates a block diagram of a mobile communication device suchas a cellular telephone or personal communication device. Mobilecommunication device 10 includes transceiver 12 which sends and receivessignals from antenna 15. Mobile communication device 10 is controlled bycontrol system 14 which may include a microprocessor or a microcomputer.Control system 14 uses memory 16 for storing programs that are executedand for storing information that is entered by the user, thedistributor, the communication services provider or the manufacturer.Information such as user preferences, user telephone numbers, preferredservice provider lists and frequency search schedules are stored inmemory 16. Memory 16 may include storage devices such as random accessmemory (RAM), read only memory (ROM) and/or programmable read onlymemory (PROM). A user communicates with control system 14 via keypad 18.Control system 14 communicates information to the user via display 20.Display 20 may be used to display information such as status informationand items such as telephone numbers entered via keypad 18. Soundinformation to be transmitted from the mobile communication device 10 isreceived via microphone 22, and sound communications received by mobilecommunication device 10 are played to the user via speaker 24.

After initially powering-up, a mobile communication device locates aservice provider and registers with the service provider. Recalling FIG.1, service providers are located at a plurality of frequency bandsacross the radio spectrum. In order to find a service provider, thecommunication device searches the spectrum to find service providers.The communications device examines received service provider code e.g.,SOCs (Service Operator Code) or SIDs (System Identification Code) todetermine whether the service provider is an optimal, preferred orprohibited service provider.

FIG. 4 illustrates a process or program that control system 14 executesin order to find a desirable service provider. After power-up, step 30is executed to initialize a non-optimal flag by clearing the flag. Step32 determines whether the last service provider, that is, the serviceprovider used before powered down, was an optimal service provider. Thisis determined by checking the SOC or SID of the last service providerand determining whether that service provider's SOC or SID correspondsto the SOC or SID of an optimal service provider. The SOC or SID of thelast service provider and a list of optimal and preferred serviceproviders is stored in memory 16. If in step 32 it is determined thatthe prior service provider was not optimal, a global spectrum search isexecuted. If the last service provider was optimal, step 34 is executedwhere system 14 attempts to lock onto the control signal of the serviceprovider. If the lock is unsuccessful, which may indicate that controlchannel is no longer available or out of range, the global spectrumsearch is executed. If a lock is successful, step 36 is executed. Instep 36, it is determined whether the control channel contains the SOCor SID of an optimal service provider. Once again, this is determined bycomparing the SOC or SID from the control signal with a list of optimalservice provider SOCs or SIDs. If the SOC or SID does not belong to thatof an optimal service provider, the global spectrum search 33 isexecuted and the identity of the frequency band in which the non-optimalSOC or SID was located is passed to global search routine 33 so as toavoid unnecessarily searching this portion of the spectrum again. If instep 36 it is determined that an optimal service provider has beenlocated, step 38 registers communication device 10 with the serviceprovider. Step 40 is an idle state where control system 14 simplymonitors the control channel of the service provider for communicationsystem overhead information and for paging information that may indicatean incoming communication. While in idle state 40, a timer is activatedwhich permits a low-duty cycle search to be performed if the phone ispresently registered in a non-optimal service provider system. Thissituation may arise if global spectrum search 33 provides a preferredbut not optimal service provider. Periodically, such as every 5 minutes,step 42 is executed to determine whether the non-optimal flag has beenset, if the non-optimal flag is not set, control system 14 returns toidle step 40. If the non-optimal has been set, step 42 leads to theexecution of periodic search routine 44 where a search is conducted inorder to attempt to locate an optimal service provider. If periodicsearch routine 44 produces an optimal service provider, the non-optimalservice provider flag is cleared and the mobile communication deviceregisters with the optimal service providers while executing periodicsearch routine 44. The mobile communications device then enters an idlestate by executing step 40. If an optimal service provider is notlocated in routine 44, control system 14 returns to an idle state byexecuting step 40.

FIG. 5 illustrates a flowchart of global spectrum search routine 33which is executed by control system 14. At step 60 it is determinedwhether the last control channel used by the mobile communication devicewas a personal communication services related control channel, that is,a control channel in the bands A through F. If the last control channelwas not a PCS control channel, step 62 is executed. In step 62 it isdetermined whether the mobile communication device can lock onto, orreceive and decode the last ACC (Analog Control Channel) that was used.If the mobile communication device can successfully lock onto the lastACC, step 64 is executed. If the communication device cannot lock ontothe last ACC, step 66 is executed. In step 66, an RSS (Received SignalStrength Scan) is performed. This step involves the mobile communicationdevice tuning to each of the 21 ACCs associated with the cellular bandof the last used ACC, and attempting to lock onto the strongest receivedsignal. In step 68, it is determined whether a lock has been achieved.In step 68 if a lock is not obtained, a predetermined search schedule isexecuted in order to find a service provider; if in step 72 a lock isobtained, step 64 is executed where the SOC or SID obtained from thecontrol channel is compared to a list of optimal SOCs or SIDs. In step70 if the received SOC or SID is associated with an optimal serviceprovider, step 72 is executed where the mobile communication deviceclears the non-optimal flags, registers with the communication serviceprovider, and then enters an idle state by executing step 40 of FIG. 4.If, in step 70 it is determined that an optimal service provider SOC orSID was not received, step 74 is executed where the identity of thefrequency band just searched is stored in memory 16. Step 78 is executedafter step 74, after 68 if a lock is not obtained, or after step 60 ifthe last control signal was from a PCS frequency band. In step 78, asearch schedule is downloaded using a master search schedule. Whendownloading the search schedule in step 80, frequency bands previouslysearched are removed from the downloaded schedule so as to avoidsearching bands that have already been searched. For example, bandssearched in the search routine discussed with regard to FIG. 4 and thecellular band search discussed with regard to step 74 are removed fromthe search schedule. After the modified search schedule has been loaded,a search pointer is initialized to point to the first band identified bythe modified search schedule. The first band identified on the modifiedschedule is searched with regard to received signal strength (RSS) instep 79's RSS routine. In the case of bands “a” and “b”, the ACC withthe strongest signal is selected. In the case of the PCS bands, that isthe bands A through F, 2.5 MHz sections of each band are searched in 30kilohertz steps. The mobile communication device tunes to the strongestsignal that crosses a minimum threshold, e.g., −110 dBm, within the 2.5MHz band being examined. In step 80 it is determined whether the signalis valid, that is, conforms to one of the above mentioned standards. Ifit is not valid, the search pointer is incremented in step 96, and ifthe signal is valid, step 82 is executed. In step 82 it is determinedwhether the signal is an ACC. If the signal is an ACC, the SOC or SID isdecoded in step 90. If the signal is not an ACC, step 84 determineswhether the received signal is a digital traffic channel (DTC) or adigital control channel (DCCH). If the signal is an DCCH the SOC or SIDis extracted in step 90. If it is determined that the received signal isa DTC, step 86 is executed where the DL (digital channel locator) isextracted to identify the location of the DCCHs associated with the DTCthat has been received. In step 88, the mobile communication devicetunes to the strongest DCCH of the digital control channels identifiedby the DL. In step 90, the SOC or SID of the received DCCH is extractedand in step 91, it is determined whether the SOC or SID is associatedwith an optimal service provider. If the SOC or SID is associated withan optimal service provider, step 92 clears the non-optimal flag andstep 96 registers the mobile communication device with the serviceprovider. After step 96, the communication device enters the idle statein step 40 of FIG. 4. If in step 92 it is determined that the SOC or SIDdoes not belong to that of an optimal service provider, step 94 isexecuted where the SOC or SID is stored in memory 16 indicating whetherthe SOC or SID was at least a preferred rather than an undesirable orprohibited service provider with the spectral location of the SOC's orSID's control channel. In step 96 the search pointer that identifies theband being searched is advanced to identify the next band in theschedule for searching. In step 98 it is determined whether the pointerhas reached the end of the search schedule. If the end of the searchschedule has not been reached, step 82 is executed to perform anotherreceived signal strength search routine as discussed above, and if thelast frequency band has been searched, step 100 is executed. In step 100the mobile communication device registers with the best stored SOC orSID, that is, an SOC or SID that has at least been associated with apreferred service provider. The best service provider can be identifiedby comparing the stored SOCs or SIDs with a list of preferred SOCs orSIDs. The list of preferred SOCs or SIDs can include the optimal SOC(s)or SID(s) and a prioritized list of preferred SOCs or SIDs where thehigher priority will get preference for registration. The listing alsoincludes undesirable or prohibited SOC(s) or SID(s) that are used onlyin emergencies (e.g., 911 calls) or if the user enters an overridecommand. After registering with the service provider in step 100, step102 is executed to set the non-optimal flag, and then step 40 of FIG. 4is executed where the mobile communication device enters the idle state.

It should be noted that the searching operation of FIGS. 4 and 5 may becarried out in a simplified manner. With regard to FIG. 4, controlsystem 14 may execute step 33 after step 30 while always skipping steps32, 34, 36 and 38. With regard to FIG. 5, control system 14 may startthe global spectrum search with step 78 while always skipping steps60-74.

FIG. 6 illustrates a flowchart for the periodic search routine executedby control system 14. In step 120 it is determined whether the periodicsearch flag has been set. If the periodic search flag has not been set,step 122 is executed where periodic search flag is set and the searchschedule is initialized by loading the master search schedule into thesearch schedule used by the periodic search routine; however, thefrequency band currently being received is not included in the searchschedule used for the periodic search routine. Step 122 also sets asearch pointer to the first band in the search schedule. In step 124 areceived signal strength search (RSS) routine is conducted. As in step79 of the global spectrum search routine of FIG. 5, step 124 is a RSSroutine of any PCS and cellular bands that are in the search schedule.In the case of a cellular band search, the 21 ACCs are searched using areceived signal strength search i.e., the transceiver tunes to thestrongest ACC. In the case of a PCS frequency band search, as discussedearlier, each band is broken into segments of approximately 2.5 MHzwhere a search of each segment is conducted in 30 kilohertz steps. Thestrongest signal within the 2.5 MHz segment and above a minimumthreshold, such as −110 dBm, is selected. In step 126 the selectedsignal is examined to determine if it is valid by conforming to one ofthe previously referenced standards. If the signal is invalid, step 144is executed and if the signal is valid, step 129 is executed. Step 129determines whether the signal is an ACC. If the signal is an ACC, step130 is executed when the SOC or SID is extracted and if the signal isnot an ACC, step 132 is executed. Step 132 determines whether a DTCsignal has been received. If the signal is not a DTC signal (thereforeit is a DCCH signal), step 130 is executed to extract the SOC or SIDfrom the DCCH signal. If in step 132 it is determined that a DTC hasbeen received, step 134 is executed to extract the DL to enable tuningto a DCCH. In step 136 a received signal strength search is conducted ofthe DCCHs where the strongest signal is selected, and then step 130 isexecuted to extract an SOC or SID from the signal. In step 138 it isdetermined whether the SOC or SID is an optimal SOC or SID. If the SOCor SID is optimal, step 140 clears the non-optimal flag and in step 142the mobile communication device registers with the service providerassociated with the optimal SOC or SID. Step 40 of FIG. 4 is thenexecuted to enter the idle state. If in step 138 it is determined thatthe SOC or SID was not an optimal service provider, step 144 isexecuted. In step 144 the search pointer is incremented to the next bandto be searched. In step 146, it is determined whether the entire searchschedule has been completed. If the schedule has not been completed,step 40 is executed so that the mobile communication device can bereturned to the idle state. If in step 146 it is determined that thesearch schedule has been completed, step 148 clears the periodic searchflag and then step 40 is executed so that the mobile communicationdevice can enter the idle state.

FIG. 7 illustrates a flow chart of the RSS routine or received signalstrength search routine which is carried out, for example, in steps 79of FIG. 5 and 124 of FIG. 6. Step 170 determines whether the band beingsearched is one of the “a” or “b” cellular bands. If a cellular band isbeing searched, step 172 is executed where the 21 ACCs are searched todetermine which is the strongest, the strongest ACC is tuned to bytransceiver 12 under the control of control system 14 and then the RSSroutine is exited. If in step 170 it is determined that a cellular bandis not being searched, step 178 tunes transceiver 12 to the beginning ofthe first 2.5 MHz band in the PCS band being searched. Step 178 alsoclears a search scratch pad memory location in memory 16. The searchscratch pad is used to record the amplitude or strength and location ofa received signal. In step 180 it is determined whether the signal beingreceived is greater than a threshold. If the signal is greater than thethreshold, step 182 is executed, if the signal is not greater than thethreshold, step 184 is executed. In step 182 it determined whether thereceived signal strength is greater than the signal strength valuestored in the search scratch pad. If the received signal is not greater,then step 184 is executed. If the received signal strength is greater,step 186 is executed and the present signal strength is recorded in thesearch scratch pad with the received signal's location in the spectrum.In step 184, transceiver 12 is tuned to a frequency 30 kilohertz higherthan the frequency at which it was tuned. Step 188 determines whetherthe new frequency extends beyond the 2.5 MHz band currently beingsearched. If the new frequency does not exceed the 2.5 MHz band, step180 is executed to once again examine received signal strength relativeto the signal strength or amplitude value stored in the search scratchpad. If in step 188 it is determined that the 30 kilohertz incrementextends beyond the 2.5 MHz band being examined, step 190 is executed. Instep 190, the transceiver tunes to the signal location specified in thesearch scratch pad. If the signal is a valid signal and can be decoded,the RSS routine is exited. If the signal is not valid or cannot bedecoded, (e.g., the signal does not conform to the above-referencedstandards) step 192 is executed. In step 192, the transceiver is tunedto the beginning of the next 2.5 MHz band within the PCS band beingsearched. Step 194 determines whether the new 2.5 MHz band extendsbeyond the PCS band currently being searched. If the new incrementextends beyond the PCS band being searched, the periodic search routineis exited. If the 2.5 MHz increase does not result in extending beyondthe PCS band being searched, step 196 is executed. In step 196, thesearch scratch pad containing signal strength measurements and signallocation information is cleared to prepare for searching another band.After step 196, step 180 is executed as described above.

FIG. 8 illustrates a master search schedule. The master schedule is usedto initialize search schedules used in the above described searchroutines. The master search schedule is stored in a memory such asmemory 16. The master search schedule can be initially programmed by themobile communication device's manufacturer, distributor or user. Itshould be noted that the first location in the search schedule is leftunprogrammed. If left blank, the blank is ignored when initializing thesearch schedules for the search routines. It is desirable for the firstlocation to be programmed with the band in which the user's home serviceprovider resides. For example, if the user has a service agreement witha service provider who is licensed to operate in PCS band B within theSID or geographical area in which the user most frequently is located,band B is programmed into the first slot of the master search schedule.If, for example, band B is programmed in the first slot, the slotoriginally containing band B is made blank. This avoids searching thesame band twice. It should also be noted that the user can vary themaster search schedule through keypad 18. Additionally, the mastersearch schedule may be reprogrammed using signals received over thewireless communication channel. For example, the mobile communicationdevice may be restricted to accepting new programming for the mastersearch schedule only from a service provider transmitting the home SIDand an optimal SOC. It is also possible to accept over the airprogramming if the service provider sends a prearranged code. It isdesirable to restrict the over the air programming through the use ofcodes, home SIDs and/or optimal SOCs to avoid unintentional orundesirable altering of the master search schedule. Over the airprogramming may be implemented using for example, logical sub-channelsof a digital control channel. The logical sub-channels have thecapability to transmit data addressed to a particular mobilecommunication device and to receive data, such as confirmation data,from the mobile communications device.

When the search schedules are initialized using the master searchschedule, it is also possible to precede the first location in themaster search schedule with other frequency bands based on, for example,the prior history of the mobile communication device's use. For example,the first location searched may be the location where the phone was lastturned off (powered down) or the location where the phone was lastturned on (powered up).

FIG. 9 illustrates a table stored in memory 16 defining the optimalservice provider's SOC and SIDs, and preferred service provider's SOCsand SIDs. The SOC or SID with the lowest number has the highest priorityand is preferred over service providers with higher numbers andtherefore a lower priority. For example, an SOC or SID with a prioritylevel 2 would be preferred over an SOC or SID with a priority level of5. The table may also include SOCs or SIDs that are undesirable orprohibited. In the case of SOCs or SIDs that are prohibited, it isdesirable to permit connection to the prohibited SOCs or SIDs when anemergency call, such as a 911 call, is attempted or when the user entersan override command. The table in FIG. 9 may be programmed by themanufacturer, by the distributor when the phone is purchased or by theuser. It is also possible to program the table of FIG. 9 over the airusing restrictions similar to those used when programming the mastersearch schedule over the air.

FIG. 10 illustrates a list of geographic identifiers with associatedfrequency bands that are prioritized based on the desirability of theservice provider operating in the band. The listing of FIG. 10 is storedin memory 16, and is used for the selection of a frequency bandcontaining a desirable service provider. After initially powering up,communication device 10 tunes to the first frequency band of thefrequency search schedule, the last used frequency band, or thefrequency band used when the device was last powered up. After tuning tothe band, the communication device monitors the control signalassociated with the band to obtain a geographic identifier such as aSID. The communication device then accesses the table of FIG. 10 inorder to determine which frequency band has a desirable serviceprovider. For example, if the device received a geographic identifiersuch as 51, the table of FIG. 10 instructs the communication device totune to frequency band C for the most desirable service provider. Thecommunication device then tunes to frequency band C and attempts toregister with the service provider operating on frequency band C. If forsome reason the device is unsuccessful in registering with a serviceprovider on frequency band C, the next highest priority frequency bandmay be used. In the case of SID 51, the next most desirable frequencyband is cellular band “b”. Once again, the communication device willtune to the frequency specified by the table and attempt to registerwith the service provider operating on that frequency band. The table ofFIG. 10 offers the frequency bands in a prioritized order. The frequencybands listed to the far left are the optimal or most desirable frequencybands, i.e., the frequency bands with the optimal or most desirableservice provider. Frequency bands listed further to the right decreasein desirability or priority until prohibited frequency bands are listedat the far right. Prohibited frequency bands may be used in emergencysituations or when overridden by the operator of the communicationdevice.

The table of FIG. 10 may be programmed into memory 16 of thecommunication device by the device manufacturer, by the distributor orby the user via the keypad. It is also possible to program the table ofFIG. 10 using over the air programming in a manner similar to that whichwas used for programming the search schedule of FIG. 8 or theprioritized table of service providers of FIG. 9. In some cases, theremay not be a geographic identifier or SID in the table of FIG. 10 for aidentifier that is received from a control channel to which thecommunication device is tuned. In this case, the communications deviceexecutes the search algorithms discussed earlier in an effort to locatea desirable service provider. When a desirable service provider has beenlocated, the table of FIG. 10 is updated to list the previously unlistedgeographic identifier and the frequency at which a desirable serviceprovider is located.

It is also possible for the communication device to locate a desirablefrequency band with a desirable service provider while the device ispowered down, i.e., the communication device is connected to a powersource, but the user has not actually turned on the power switch. Duringthis powered down condition, the communication device executes thesearch algorithms discussed earlier; however, the device does notregister with a service provider once a desirable service provider islocated. It is also possible for the device to locate a desirableservice provider while in the powered down condition using geographicidentifiers as discussed above. Once the device is powered up, i.e., theuser turns on the power switch, the communication device can immediatelyregister with the previously located desirable service provider andthereby minimize the amount of time the user must wait before making acall. While in the power down condition, the communication device checkson a long duty cycle, such as every five minutes to determine whetherthe desired service provider is still available. If the desired serviceprovider is not available, the communication device once again executesthe above described search algorithms to find the frequency band withthe desirable service provider. The user may disable this powered downsearching function through a keyboard command.

The invention claimed is:
 1. A method by which a powered downcommunication device locates a wireless service provider in amulti-service provider environment, comprising the steps of: tuning to afirst frequency band according to a frequency band search schedule whilepowered down; receiving a received geographic identifier from a serviceprovider in the first frequency band; comparing the received geographicidentifier to a listing of stored geographic identifiers in order toattempt to locate a matching stored geographic identifier, each of thestored geographic identifiers being associated with a desirablefrequency band having a desirable service provider; examining frequencybands according to the frequency band search schedule while powered downuntil a second frequency band having the desirable service provider islocated, the examination being carried out if the step of comparing thereceived geographic identifier does not produce the matching storedgeographic identifier; and updating the listing of stored geographicidentifiers so that the second frequency band is associated with thereceived geographic identifier; and registering with the acceptableservice provider when powered up.
 2. The method of claim 1, wherein thestep of receiving the received geographic identifier comprises receivinga system identifier code from a wireless service provider.
 3. The methodof claim 1, further comprising the step of modifying the listing ofstored geographic identifiers using information transmitted over awireless interface.
 4. The method of claim 1, further comprising thestep of modifying the listing of stored geographic identifiers usinginformation from a keypad.
 5. The method of claim 1, wherein the step ofexamining frequency bands comprises examining a plurality of frequencybands in an order specified by the frequency band search schedule. 6.The method of claim 5, further comprising the step of modifying thefrequency band search schedule using information transmitted over awireless interface.
 7. The method of claim 6, further comprising thestep of modifying the frequency band search schedule using informationfrom a keypad.